1. Field of the Invention
The field of the present invention relates to devices and methods for generating light, and more particularly to electrodeless plasma lamps energized by microwave radiation and having a solid dielectric waveguide integrated with at least one transparent bulb, wherein heat energy from the plasma is recycled into the bulb(s), resulting in high efficiency operation.
2. Related Art
Our '718 application discloses a “dielectric waveguide integrated plasma” lamp (DWIPL) including a “dielectric waveguide,” viz., a waveguide coupled by a microwave probe to a source of microwave power and having a body consisting essentially of dielectric material and a side with a lamp chamber extending into the body. The source operating frequency and waveguide body dimensions are selected such that the body resonates in at least one resonant mode having at least one electric field maximum. The lamp further includes a bulb disposed within the chamber. Thus the body, chamber and bulb are integrated as a unitary structure. The bulb contains a fill mixture (“fill”) that forms a light-emitting plasma when microwave power is directed by the waveguide into the bulb. The '718 application also discloses a DWIPL including a dielectric waveguide and two microwave probes. One probe, connected to a feedback means coupled between the probe and microwave source, probes the waveguide body to instantaneously sample the field amplitude and phase and provides this information via the feedback means to the source which dynamically adjusts the operating frequency to maintain at least one resonant mode within the waveguide body, thereby operating the lamp in a “dielectric resonant oscillator” mode. The '718 application further discloses DWIPL embodiments which differ according to waveguide body shape, bulb type (a hermetically sealed envelope vis-a-vis a bulb which is self-enclosed), number of bulbs (one vis-a-vis two), number of lamp chambers (one vis-a-vis two), and number of probes (one vis-a-vis two).
A continuation-in-part application Ser. No. 10/356,340 (“'340”), published as Pub. No. 2003/0178943 A1 and entitled “Microwave Energized Plasma Lamp With Solid Dielectric Waveguide,” discloses advances in design of the “drive probe” which supplies microwave power to the fill, and of the “feedback probe”, as well as utilization of a “start probe” to mitigate over-coupling of the drive probe, and amplifier and control circuits for two- and three-probe configurations which minimize power reflected from the body back to the source both before a plasma is formed and after it reaches steady state. The '340 application further discloses techniques for sealing a waveguide body cavity (viz., a lamp chamber) with a window or lens allowing seals to withstand large thermomechanical stresses and chamber pressures which develop during lamp operation, alternative techniques for DWIPL assembly, and waveguide bodies having two solid dielectric materials.
The '718, '340 and '788 applications asserted that quartz bulbs are unsuitable for plasma lamps of the present invention because they would be prone to failure in the 1000° C. temperature regime a bulb wall containing a plasma would experience and, even if structural failure did not occur, would be unstable in their mechanical, optical and electrical properties over long periods when repeatedly cycled in temperature. The conclusion was that use of a quartz bulb would likely result in a lamp prone to early failure. However, we have recently demonstrated that quartz can be a suitable bulb material when used in the lamp embodiments disclosed herein, and moreover provides significant advantages that an opaque fill envelope or self-enclosed bulb cannot.